The present application relates generally to the treatment of parasite infestations and, more particularly, to methods and composition to treat lice infections.
Pediculosis capitis (head lice) is an infestation of Pediculosis humanus, the human louse. This insect is transmitted to noninfected individuals through shared clothing and hairbrushes. Once present on the head, the adult female louse has a lifespan of about 25 days and lays up to 10 eggs each day which are attached to the hair shaft with a strong cement. Eggs hatch within 7-9 days producing more adult lice which continue the cycle. As the lice feed, they inject their digestive juices and fecal material into the skin and these "bites" cause pruritus.
In the past, chemical agents, including insecticides, have been used to treat pediculosis. These compounds include cholinesterase inhibitors such as neostigmine (Merch Index, Tenth Edition, entry no. 6311) or prostigmine (Merch Index Tenth Edition, entry no. 6311), and range from fairly toxic (thepyrethrins, Merch Index, Tenth Edition, entry no. 7865) to very toxic (lindane (Merch Index, Tenth Edition, entry no. 5329), malathion (Merch Index, Tenth Edition, entry no. 5522). All methods involve the exposure of the scalp and hair to these agents in shampoos or creams which are washed off relatively quickly.
While these current treatments are generally effective at killing the adult lice and eggs (nits), the dead nits remain firmly attached to the hairs after treatment. this is unsettling to the patient, as well a significant cosmetic problem. The only current means of removing dead nits is with a fine-toothed comb or forceps. These methods are time consuming and less than certain.
Formic acid, CH.sub.2 O.sub.2, is an acid produced by ants through a distillation process. It can also be made by heating carbon monoxide and NaOH under pressure and decanting the resulting sodium formate with sulfuric acid (H.sub.2 SO.sub.4). Formic acid is a colorless liquid that is irritating to the skin. It has, however, been used in cosmetics (0.05%-0.2%) as a preservative or an astringent.
It has been found, surprisingly, that formic acid is useful in the treatment of pediculosis in that concentrations of formic acid from about 1% to about 25% can be used to remove dead nits from hair without producing undue damage to hair or skin. This "nit removing" activity of formic acid can be observed and utilized clinically either by incorporating formic acid by itself into a shampoo or rinse for use after a pediculicide preparation or by incorporating formic acid into the shampoo, lotion, or cream containing the active pediculicide.